1. Field of the Invention
The present invention relates to a fuel cell system with a combustor provided therein.
2. Description of the Related Art
There has been proposed a technique for a fuel cell system with a combustor provided therein, in which both an anode off-gas exhausted from an anode electrode (a hydrogen electrode) and a cathode off-gas exhausted from a cathode electrode (an air electrode) of a fuel cell are introduced to a combustor, and exhaust heat generated by the combustion reaction of the two gases is introduced in a heat exchanger to heat a cooling medium, and thus warms up the fuel cell at a startup at low temperature (See Japanese Published Patent Application No. 2004-179153, paragraph 0023, FIG. 1). There has been proposed another technique for a fuel cell system with a combustor provided therein, in which an anode off-gas flow passage is provided with a flow passage branching from an upstream side of a fuel cell for introducing an anode gas before being subjected to reaction in a combustor, and likewise, a cathode off-gas flow passage is provided with a flow passage branching from the upstream side of the fuel cell for introducing a cathode gas before subjected to reaction into the combustor (See Japanese Published Patent Application No. 2004-95258, paragraph 0011, FIG. 1).
The technique described in Japanese Published Patent Application No. 2004-179153 uses, in the meantime, the off-gases having passed through a fuel cell for combustion. The use of the off-gases makes it difficult to control combustion at a target temperature, because individual quantities of hydrogen and oxygen in the off-gases cannot be accurately measured. In addition, it is necessary for the off-gases to be subjected to reaction both in a fuel cell and a combustor. Then, each supply quantity of hydrogen and air needs to be increased as compared to a case in which the off-gases are reacted only in a fuel cell, resulting in an increase of energy required during the supply. Also in Japanese Published Patent Application No. 2004-95258, the off-gases are used for combustion, which makes combustion control difficult.
An object of the present invention is to solve the problems described above, and thus to provide a fuel cell system capable of appropriately controlling combustion even when the system starts up at low temperature, and of efficiently warming up a fuel cell thereof.